Note that running SPA on superpixels rather than raw pixels improves performance significantly here, since averaging signals within superpixels boosts SNR (making it easier to separate signal from noise and isolate pure from mixed pixels) and also greatly reduces the dimensionality of the non-negative regression problem SPA has to solve at each iteration. (To keep the problem size small we also run SPA just on small local spatial patches, as in the previous section.) Finally, while we have obtained good results with SPA, other approaches are available [1]} and could be worth further exploration in the future. See Figure REF  for a visual summary of the full procedure.
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